合作式阿羅哈協定在衰弱通道下

Abstract

當原始的媒體接取控制協定應用在衰弱通道下，信號傳輸可能會中斷，以至於降低系統生產量。為了抵抗這個通道帶來的損失，對媒體接取控制協定而言，使用者合作所帶來的合作式多樣性被視為是有效的解決方法。以前在合作式媒體接取控制協定上的成果，主要專注在提升鍊結的可靠性（多樣性合作模式），卻忽略掉使用者合作是可以幫助提升系統生產量的。為了達到這個目的，我們提出了新的合作式媒體接取控制協定，能讓來源使用者將其封包換手給接替使用者，而自己轉而去處理新的封包（多工合作模式）。為了將這個概念應用到原始的媒體接取控制協定，進而提升系統生產量，我們在這篇論文中提出了合作式阿羅哈協定（CAP）在衰弱通道下。然而，我們發現所提出的新的合作式媒體接取控制協定只能在某些條件下有利於系統效能。不過，藉由新舊合作式媒體接取控制協定之間的互補特性，我們得知兩種合作模式之間有交換性質存在。因此，我們提出了基於門檻條件的穩定化技術，去監控整體的流量負載，並以之選擇合作模式。模擬結果顯示，穩定化後的CAP能勝過以往的阿羅哈協定。

As original MAC protocols are applied in fading channels, the signals transmission may fall in outage and thus the system performance is degraded. To combat this channel impairment, user cooperation providing cooperative diversity has been considered as a promising technology for MAC protocols. Previous efforts on cooperative MAC protocols primarily focus on improving link reliability (Diversity cooperation mode), which ignore that user cooperation can help improve the system throughput as well. To this end, we propose a new cooperative MAC protocol which enables the source to handover its packet to the relay node so that it can turn to cope with its new packets (Multiplexing cooperation mode). In order to apply such concept onto original MAC protocols, so as to enhance the system throughput, we propose cooperative ALOHA protocol (CAP) in fading channels in thesis. However, it is shown that the proposed cooperative MAC protocol benefits to the system performance conditionally. By the complementary properties of the conventional and the proposed cooperative MAC protocol, we observe that there is a tradeoff between the cooperation modes. Therefore, a threshold-based stabilization technique to monitor the aggregate traffic load so as to select cooperation mode accordingly is proposed. Simulation results show that the stabilized CAP can always outperform the conventional ALOHA protocol.